Reciprocating internal combustion (IC) engines are known for converting chemical energy stored in a fuel supply into mechanical shaft power. A fuel-oxidizer mixture is received in a variable volume of an IC engine defined by a piston translating within a cylinder bore. The fuel-oxidizer mixture burns inside the variable volume to convert chemical energy from the mixture into heat. In turn, expansion of the combustion products within the variable volume performs work on the piston, which may be transferred to an output shaft of the IC engine.
Variations in the temperature and the chemical composition of an oxidizer stream entering an engine are known to affect engine performance. For example, exhaust gas recirculation (EGR) may be used to modify the temperature of an oxidizer stream, a chemical composition of an oxidizer stream, or combinations thereof, by combining a portion of exhaust gas with an oxidizer stream entering an engine
Further, variations in the pressure of an oxidizer stream entering an engine are also known to affect engine performance. As a result, some engine systems employ turbochargers or superchargers to increase the pressure of the oxidizer stream entering the engine. Some conventional approaches to turbocharging may include more than one turbocharger.
U.S. Pat. No. 7,165,403 (“the '403 patent”), entitled “Series/Parallel Turbochargers and Switchable High/Low Pressure EGR for Internal Combustion Engines,” purports to address the problem of turbocharger sizing and inertial lag or delay. The '403 patent describes systems and methods for turbocharging and providing exhaust gas recirculation for internal combustion engines.
The engine system of the '403 patent includes a first turbocharger associated with a first bank of engine cylinders and a second turbocharger fluidly coupled to the first turbocharger. The first turbocharger preferably has a variable geometry, such as a variable turbine inlet nozzle, to improve efficiency and boost for low mass flow operating regions while maintaining high mass flow capacity at higher engine speeds. Further, exhaust system valving in the '403 patent may be actuated to operate the first turbocharger and the second turbocharger in series operation or parallel operation, where the outlet of the first turbine is blocked from fluid communication with the inlet to the second turbine during parallel operation.
However, the variable geometry turbochargers recommended by the '403 patent may be unduly expensive, complex, physically large, or combinations thereof. Further, the series and parallel operation of the two turbochargers may not optimize all desired engine operating conditions. Accordingly, there is a need for improved exhaust systems to address the aforementioned problems, other problems in the art, or combinations thereof.